The present invention relates to a method and apparatus for extracting a liquid from an underground reservoir. The invention is particularly applicable with respect to extracting oil from the ground, and is therefore described with respect to that application, but it will be appreciated that it would be used for extracting other liquids, for example water.
In one method of extracting oil from an underground reservoir, the reservoir energy is utilized to transport the liquid through the underground reservoir to the well bore, and then to raise the liquid in the well bore to a level, called the dynamic level. Conventional pumps are then operated to raise the liquid from the dynamic level to the surface.
The above method of extracting oil frequently results in the depletion of the reservoir energy before extracting all or even most of the oil, leaving a substantial percentage in the ground without natural propulsive energy. Secondary recovery methods may sometimes be used to extract additional oil, but these methods are expensive and not always commercially feasible.